The present invention relates generally to subterranean well systems having multiple tubular strings installed therein and, in one embodiment described herein, more particularly provides a dual string completion system utilizing an improved wye block.
It is well known in the art to interconnect an upper tubular string to multiple lower tubular strings in a subterranean well utilizing a device known as a wye block. The wye block typically has an upper threaded connection for attachment to the upper tubular string, and multiple lower threaded connections for attachment to the multiple lower tubular strings. In this manner, fluid communication is established between the upper tubular string and each of the multiple lower tubular strings so that, for example, fluids from different formations or zones intersected by the well and produced through corresponding ones of the multiple lower tubular strings may be flowed to the earth's surface via the upper tubular string.
The wye block derives its name from the fact that it has a generally Y-shaped body or housing when it is configured to interconnect a single upper tubular string to two lower tubular strings. In a more general sense, and as used herein, however, the term "wye block" includes configurations in which two or more tubular strings are interconnected to another tubular string by the wye block body or housing. Additionally, the term "wye block" is not restricted to configurations in which a single tubular string extends in an upward direction therefrom and multiple tubular strings extend in a downward direction therefrom, although this may be the most commonly used configuration.
As stated above, the typical wye block provides fluid communication between the interconnected tubular strings via their attachment to the wye block body or housing. However, providing convenient access between each of the tubular strings is a far more difficult proposition. For example, if it is desired to convey a wireline tool or a coiled tubing string from the earth's surface into a certain one of the lower tubular strings, a device or mechanism should be provided in the wye block to direct the wireline tool or coiled tubing string from the upper tubular string, into the desired one of the lower tubular strings, and not into any other of the lower tubular strings. In addition, the device or mechanism should be capable of being repositioned when it is desired to permit access to another selected one of the lower tubular strings. Furthermore, the device or mechanism should not impede flow through the wye block during fluid production from the well, and should be reliable in operation, convenient to operate, and not subject to damage and deterioration during wellbore operations.
One proposed method of accomplishing these objectives is to construct the wye block with a diverter mechanism therein. The diverter mechanism may be a type of hinged flapper which, when positioned to one side in the wye block, will divert the tool or coiled tubing string toward a selected one of two lower tubular strings and, when positioned to the other side in the wye block, will divert the tool or coiled tubing string to the other lower tubular string. Openings may be provided in the flapper to permit fluid flow therethrough.
Unfortunately, such diverter mechanisms have several shortcomings. For example, the hinged flapper is subject to erosion and other deterioration, due to substantially constant fluid flow therethrough. Debris may accumulate about the diverter mechanism, preventing its subsequent operation. The openings formed through the flapper are typically not equivalent to a full bore opening. Only two lower tubular strings may be selected among by the diverter mechanism. In addition, a positive indication at the earth's surface is usually not available for determining whether the diverter mechanism has actually selected the desired lower tubular string for access thereto.
In view of the foregoing, it will be appreciated that a need exists for an improved wye block and improved methods of servicing wells in which multiple tubular strings are interconnected.